Stability of the Surface Electron Accumulation Layers on the Nonpolar (1010) and (1120) Faces of ZnO

Robert Heinhold, Simon P. Cooil, D. Andrew Evans, Martin W. Allen

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Abstract

The stability of the hydroxyl termination and downward band bending on the m-plane (101̅0) and a-plane (112̅0) faces of ZnO single crystals was investigated using synchrotron and real-time X-ray photoelectron spectroscopy. On these nonpolar surfaces, a strong correlation was found between the surface band bending and the surface OH coverage, both of which could be modified via heat treatment in ultra high vacuum (UHV). On the m-plane (101̅0) face, in particular, a threshold temperature of ∼400 °C was observed, after which there was a sudden increase in OH desorption and upward movement of the near-surface bands, resulting in a metallic-to-semiconductor transition in the electronic nature of the surface, with a change from surface electron accumulation to depletion. This loss of surface metallicity is associated with the disruption of a stable monolayer of chemisorbed hydroxyl groups that form a closed hydrogen-bonded network, across rows of Zn–O dimers, on the m-plane (101̅0) face. The surface electron accumulation layers on both the m-plane (101̅0) and a-plane (112̅0) faces can be modified and eventually removed by simple UHV heat treatment, with important implications for the electrical properties of ZnO nanostructures and catalytic ZnO nanopowders, which contain a high proportion of these nonpolar surfaces.
Original languageEnglish
Pages (from-to)24575-24582
Number of pages8
JournalJournal of Physical Chemistry C
Volume118
Issue number42
Early online date13 Oct 2014
DOIs
Publication statusPublished - 26 Oct 2014

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